1. Field of the Invention
The present invention relates to the debromination of dibromonaphthalene compounds and, more especially, to the monodebromination of dibromonaphthalene compounds having the formula: ##STR2## wherein R is hydrogen, an alkyl, aryl, aralkyl or ##STR3## radical, with R' itself being an alkyl radical, by regio-selective catalytic hydrodebromination.
The final products of such debromination reaction thus have the formula: ##STR4## in which R is as defined above.
2. Description of the Prior Art
The 6-bromonaphthalenes of formula (2) above are known and valuable compounds. For example, 6-bromo-2-methoxynaphthalene is widely used for synthesizing naproxen or nabumetone, two pharmaceuticals which are well known for their therapeutic anti-inflammatory properties, and also for synthesizing methallenestril, which is an estrogen (compare The Merck Index, eleventh edition, pages 1002, 1014 and 937 (1989)).
As regards 6-bromo-2-hydroxynaphthalene (also referred to as 6-bromo-.beta.-naphthol), this is principally used for synthesizing the aforesaid 6-bromo-2-methoxynaphthalene via alkylation by means of dimethyl sulfate or methanol.
According to EP-A-179,447, 6-bromo-2-[hydroxy or alkoxy]naphthalenes may be prepared by stoichiometric metallic reduction of the corresponding 1,6-dibromo-2-[hydroxy or alkoxy]naphthalenes by the following reaction: ##STR5## in which X is hydrogen or an alkyl radical, and M is a reducing metal such as iron or tin. The above dibrominated compounds may themselves be simply prepared by direct bromination of the corresponding non-brominated compounds: ##STR6## However, reducing dibrominated derivatives of naphthalene to monobrominated derivatives by a method as described above presents the disadvantage, inter alia, of requiring large amounts of metal, which metal is ultimately present in the reaction effluent which is difficult to salvage and often becomes a pollutant, such as FeBr.sub.2.
Moreover, the yield of the desired monobrominated compounds from such a process may prove to be inadequate.